Cereal grains are a dietary staple in almost every human community and are a source of protein and complex carbohydrates. Cereals contain a high content of starch and cellulosic fiber, and significant amounts of protein.
Throughout their long use as a food staple, cereal grains have been subjected to numerous enzymatic modifications to improve their functionality, primarily by converting starch contained in the cereal product to more easily assimilable or palatable forms. Conversion of fiber in cereals to different forms has received less, but significant, attention in the past because the major portion of fiber can be removed from grains in the grain milling process.
In those processes known in the art in which the cellulose content of the cereal grain is treated, the modifications are primarily directed to improving the accessibility of the starch fraction of the grain for further processing or for recovery of food value from a removed fiber fraction.
In Japanese Publication No. 53-62848, rice is subjected to digestion of cellulose or hemi-cellulose by a solution of enzymes, such as hemi-cellulase, pectinase and cellulase, and solid material is separated from the enzyme solution. The solid material is boiled with water to yield a liquid food.
Japanese Publication No. 57-47363 teaches the production of a cereal tea by treating cereal grains with heat between 100.degree.-200.degree. C. to puff the cereal, followed by treatment with an enzyme such as cellulase. The enzymatically treated cereal is heat dried and than roasted.
U.S. Pat. No. 4,089,745 discloses the treatment of corn hull cellulose with alkali to obtain three fractions and the conversion of the treated cellulose fraction to glucose.
U.S. Pat. No. 4,247,636 discloses treating a mixture of water and flour with .beta.-glucanase to produce a relatively low viscosity slurry which is treated with amylase, glucoamylase and glucose isomerase to produce a high fructose sweetener.
A process for silage treatment is described in U.S. Pat. No. 4,292,331. Silaged vegetable matter is exposed to enzymes and bacteria or fungi that produce hemi-cellulases, amylase and amyloglucosidase. These enzymes may be suspended on a starch support prior to adding to the vegetable matter. Fermentable sugars are produced which are in turn fermented to lactate by lactobacilli.
In U.S. Pat. No. 4,378,432, vegetable matter is treated with phosphoric acid to hydrolyse cellulose and then enzymes capable of hydrolyzing cellulose and hemi cellulose to produce reducing sugars, whereby a sweetened aqueous solution is obtained.
U.S. Pat. No. 3,395,019 discloses the production of animal feed from oat hulls by treatment of oat hulls, mixed with 50 to 70% water by weight, with alkali, yeast, or enzymes such as catalase, cellulase or amylase. The treatment increases absorbency of the oat hulls for liquid nutrients such as molasses.
U.S. Pat. Nos. 4,431,674 and 4,435,430 disclose enzyme saccharified cereals made from whole grain cereal. In this process, the whole grain is milled and the germ, bran and endosperm fractions are separated. The bran fraction is treated to increase its functionality and endosperm fraction is separately treated enzymatically with .alpha.-amylase and glucoamylase. The fractions are then recombined. Bran treatment is disclosed as critical to the process, but simultaneously treating all of the cereal fractions enzymatically is taught as decreasing the quality of the dough.
U.S. Pat. No. 2,555,235 teaches the treatment of grain endosperm by steeping vacuum-treated grain in a grain extract at a temperature and pressure to promote enzymatic action. Among the enzymes present in the grains are cellulase and several amylases and glucosidases.
In the present invention, the cellulose component of a flour or meal comprising starch and cellulose fiber, is enzymatically altered to saccaharify the cellulose, and to produce fructose in the treated flour or meal under conditions in which substantially all of the fructose so produced and all, or a substantial portion, of the starch are retained.